Letitia Baldrige, the imposing author, etiquette adviser and business executive who became a household name as Jacqueline Kennedy’s White House chief of staff, died Monday in Bethesda, Md. She was 86.

Her death was confirmed by Mary M. Mitchell, a longtime friend and collaborator.

At 35, Baldrige, known as Tish, left her job as public-relations director for Tiffany & Co. to help out a friend and fellow Vassar alumna, the former Jacqueline Bouvier, becoming, in essence, the social secretary of the Kennedy White House as it emerged as a center of culture, art, youthful elegance and sparkling state dinners.

Baldrige left the White House in June 1963, less than six months before President John F. Kennedy’s assassination, to work for the Merchandise Mart, a Kennedy family business in Chicago. She went on to found her own public relations and marketing business.

In the 1970s she established herself as an authority on contemporary etiquette, writing a syndicated newspaper column on the subject and updating “Amy Vanderbilt’s Complete Book of Etiquette” in 1978, less than four years after Vanderbilt’s death. Baldrige’s face soon appeared on the cover of Time magazine, which hailed her as the nation’s social arbiter.

After that, her own name was enough to attract readers, and in 1985 she published “Letitia Baldrige’s Complete Guide to Executive Manners,” which dealt with behavior in the workplace and outside it. In that book, she declared it acceptable to cut salad with a knife. She recommended that whoever reaches the door first — either man or woman — open it. And she suggested infrequent shampooing when staying on a yacht, to conserve water.

Baldrige, who stood 6 feet 1 inch tall and became known for her elegant silver hair, long contended that the heart of all etiquette was consideration for others, rather than a rigid set of rules.

“There are major CEOs who do not know how to hold a knife and fork properly, but I don’t worry about that as much as the lack of kindness,” she told The New York Times in 1992. “There are two generations of people who have not learned how important it is to take time to say, ‘I’m sorry’ and ‘please’ and ‘thank you’ and how people must relate to one another.”

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